Plasmopara halstedii, cause of downy mildew of sunflower, is a pathogen of worldwide economic importance. Efforts to amplify the ITS-region from this organism revealed an unexpected fragment length of about 2600bp, in contrast to about 900bp, reported for other members of the Peronosporaceae. First attempts to obtain the complete sequence of the P. halstedii fragment were unsuccessful, due to
... [Show full abstract] repeated elements in ITS, which were uncovered later on. The presence of a single EcoRI-site allowed us to apply a restriction-ligation procedure to amplify parts of the ITS fragment separately. Sequencing of these fragments revealed the presence of four copies of a tandemly arranged repetitive element in the ITS-2 region. The complete sequence was obtained by using a sequencing primer which annealed shortly before the repetitions so covering the gap in the sequence around the restriction site. The ITS sequence in P. halstedii (AY773346) consisted of 2587bp in total, with ITS-2 accounting for 2212bp alone. This is the longest ITS-2 sequence reported so far for any examined species.
